Eugene d



E. D. EBY.

iNSULATlNG BUSHING.

APPLICATION FILED MAY 24. 1918.

Patented May 20, 1919.

u b EL 0. mD e n me Q u E UNITED STATES PATENT OFFICE.

EUGENE D. EBY, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INSULATIN G-BUSHIN G.

Specification of Letters Patent.

Application filed May 24, 1918. Serial No. 236,270.

To all whom it may concern Be it known that I, EUGENE D. EBY, a citizen of the United States, residing at Pittsfield, county of Berkshire, State of Massachusetts have invented certain new and useful Improvements in Insulating Bushings, of which the following is a specification.

. My invention relates to insulating bushings for insulating high potential leads from casings which inclose electrical apparatus and has for its object the provision of an improved construction therefor to resist surges, corona and other transient phenomena.

In incased electrical apparatus which are submerged in oil, it has been customary to have the insulating bushin insulating the lead from the casing, extenf into the casing. with the lead passing from the interior end connected to the electrical apparatus, so that there was a gradual drop in the potential or definite potential gradient from the, exterior end of the bushing to the casing, over the interiorly exposed surface of the bushing. Should a surge or the like occur on the hne, a corona. would appear over the surface of the bushing, together with the consequent brush discharge -to the .casing. This discharge is objectionable, particularly over the surface of the oil surrounding the incased electrical apparatus, where an explosive m1x-. ture may have formed, so that grounded metallic surfaces have been used to protect the inner ends of bushings and to eliminate the occurrence of corona and .brush discharge in the interior of oil filled casings (the term oil as hereinafter used being understoodto include such other insulating media as may be used instead of oil); the lower end I submerged beneath' the oil so that the lead emerging therefrom traverses only a medrum having a much greater dielectric strength than air orthe gas above the 011 surface thereby maintaining the protected surface of the bushing above the oil at substantially zero potential.

In the practice of my invention I have so formed and mounted the protectin metallic surface or shield that the entire ushing surface from the cover of the casing to the surface of the oil is free from both mechanical and ammo strains r I a a d unbroken insulating surface,

of-such metallic surface being such shield directly on the surface of an interiorly pro ecting portion. of the bushing with rolled back ends, which projecting portion is mounted in the outer portion of the bushing so that the shield is supported by an thereof being sustained by the cover.

For a more complete understanding of the nature and objects of my invention, reference should be had to the following detailed description taken in connection with the accompanying drawing in which Figure 1 shows an insulating bushing partlyin sec-- tion and partly in elevation constructed in accordance with my invention; Fig. 2 is an enlarged vertical section of a portion of the bushing; while Fig. 3 is an enlarged section taken on the line aa in Fig. 1.

Referring now to the drawing, 10 denotes 7 a metallic collar to which the bushing structure is secured in any suitable which serves as a convenient means for securing the bushing structure-to the metallic casing 9 inclosing electrical apparatus, such as a transformer, with whose windings the conductor in the bushing is to be connected.

The insulating member 11 is hereshown at 12 as cemented to the collar 10, and is preferably provided with a petticoat structure 13. The insulatin member 11, which is hollow and is prefera ly made of molded porcelain, has a metallic cap 14 rigidlv secured thereto,

as by cement; the cap 14 being given a generally rounded contour so as to avoid sharp edges and thereby avoid undue electrostatic strains near the end of the bushing.

To the cap 14 is secured the terminal member 15 having a cup 16, in which the aerial conductor (not shown) may be brazed or otherwise secured, and is also provided with the interior socket 17 in which the interior conductor 18 is secured.

The conductor 18 is protected by a metallic tube 19 secured in a central hub portion 20 of the cap 14. The tube 19'has formed about it a uniform cylinder 21 of fibrous insulating material. The cylinder 21 is consequently supported in a pendent position from the top of the member 11 and is preferably formed slightly conical at its upper end where inserted in the insulating member 11, as shown at 22.

That portion of the insulating cylinder 21, which is designed to constitute the interiorly the Weight 60 manner and 7 I strains.

lic surface or shield 25, which is, in turn,-

overlaid by another layer of insulating material 26.

The shield 25 is grounded on-the collar 10, and consequently on the casing, by the conducting connection 27 Both ends of the ground shield 25 are rolled back, as

indicated at 29 and 30, so as to relieve the electrostatic strain at these points, which rolled ends are conveniently bound inplace by rolling back the under layer of insulating material 24; the rolled ends being supported in distended position by means of fillers'31 and 32 of insulating material.

. The upper rolled edge 30 of the shield 25 conveniently projects slightly into the hollow insulating member 11. The end 25 and the cylinder 21 are held in place by a hardened filling of insulating material 33, which may be poured into the member 11 when in a plastic condition.

This material 33, while plastic, may conveniently be poured. into the insulating member through one or more openings 34 which are formed in the central hub portion 20 of the cap 14.

An insulating bushing, such as I have described, prevents theoccurrence of corona and brush discharge in tanks for electrical apparatus because the entire interiorly ex posed surface of the bushing from the easing to the surface of the oil is at substantlally zero potential by reason of the ground shield 25; the oil level, in practice,

being kept at such a height that the lower end of the ground shield is submerged for a distance of from 3 to 4 inches.

It will be seen that the whole weight of the ground shield 25 and that of the en. shrouded cylinder 21 is borne by the insulating member 11 and is transmitted therethrough asa compressional strain to the cover of metallic casing 9 The shield 25 is itself free from mechamcal strains since it laid complete over the even surface of cylinder 21 prior to assembly, the, ends being rolled back to avoid undue electrostatic strains at the .ends, so that when electrically connected to the collar 10 or other ground connection the entire interior surface above the oil not only of the bushin'g'but of the tank itself will be at zero potential and substantially free from both mechanical and electrical While I have here shown an embodiment of my invention which is at present the best means known to me for carrying the same into efiect, I would have it under tood that this is merely illustrative and that I do not mean to be limited thereby to the precise details here disclosed, since obvious alteratlons thereof will appear to those skilled in this art, nor in the choice of recognized equivalents except as defined in my claims hereunto annexed.

- What '-I clalm as new and desireto secure by Letters Patent of the United States,

1. An insulating bushing for oil submerged electrical apparatus comprising an insulating member having a terminal securing device secured to one end, a second insulating member secured in the first insulating member and projecting from its other end, said second insulating member adapted to have its lower end submerged beneath the oil surface and formed with a lead opening therein, and a grounded shield overlaid with a layer of insulating material e'nshrouding the whole exposed surface of said second insulating member which is above the'oil surface.

2. An insulating bushing for oil sub merged electrical apparatus comprising an insulating member having a terminal securing device secured to one end, a second insulating member secured in the first insulating member and projecting from its other end, said second insulating member adapted to have its lower end submerged beneath the oil surface and formed with a lead opening therein, and a grounded shield having. its ends olled back and bound in place with layers of insulating material; said grounded shield enshrouding the whole exposed surface of said second insulating member which is above the oil surface.

3. An, insulating bushing for oil submer ed electrical apparatus comprising an in ating memberhavinga terminal securing device secured to one end, a second insulating member secured in the first insulating member and projecting from the other end thereof, said second insulatingmember adapted to have its lower end submerged beneath the oil surface and formed with alead opening therein, a grounded. shield having its ends rolled back, fillers of insulating material holding. said rolled ends in distended position, and a layer of insulating cylinder in said insulating member, and an electrical connection between said shield and collar.

5. An insulating bushing for 'oil submerged electrical apparatus comprising an insulating member having a terminal securenshrouding that portion of the surface of said cylindrical insulating member which is to be exposed above the oil level, one end thereof projecting slightly into the first said insulating member, a hardened filling of insulating material for rigidly supporting said shield and cylinder in the first said insulating member, and an electrical connection between said shield and said collar.

6. The combination with a casin 'for oil submerged electrical apparatus, 0? a conducting lead, and a bushing therefor comprising an insulating member secured exteriorly of said casing, a second insulating member secured in said first member and projecting pendently therefrom .into said casing having its lower end submerged beneaththe surface of the oil, and a metallic 1 shield rounded on said casing enshrouding the entlre surface of said second insulating member between said casing and the oil surface..

submerged electrical apparatus, 0

7. The combination with a casin' for oil a conducting lead, and a bushing therefor comprising an insulating member secured exteriorly of said casing, a second insulating member secured in said first member and projecting pendently therefrom into said casing having its lower end submerged beneath the surface of the oil, and a metallic shield grounded on said casing having rolled ends and overlaying the entire surface of said second insulating member between said casing and the oil surface as one unbroken mass, and a layer of insulating material bindino' said shield and rolled ends in place. 8 T e combination with a casin for oil submerged electrical apparatus, 0 a conducting lead, and a bushing therefor comprising an insulating member secured exteriorly of said casing, a second insulat' member secured in said first member an projecting pendently therefrom into said casing having its lower end submerged beneath the surface of the oil, a supporting collar on the firstsa'id insulating member secured to said casing, a metallic shield havving rolled ends enshronding the entire surface of said second insulating member between the casing and the oil surface, and an.

electrical connection between said said collar.

In witness whereof, I have hereunto set my hand this 23rd day of May, 1918.

EUGENE D. EBY.

shield and 

